I’m contemplating doing my final paper on some aspect of cancer research, either current treatments of adult acute myeloid leukemia or something more specific such as the cancer preventative actions of tea extracts.
Due to the successful trials using animals as models, several questions are posed regarding finding and isolating the active compounds and their mechanisms and whether it can apply to humans.
Tea constituents and their biochemical properties
Briefly states the quantity of tea typically consumed and the percentage of different tea currently made world-wide. Also list various compounds and components in tea such as catechins and caffeine among others and their relative percentage by weight in green or black tea.
Recounted several recognized properties of tea polyphenols such as their ability to bind to various biomolecules.
Inhibition of carcinogenesis by tea in animal models
Touches upon how there are many different animals models used in different labs which has cancer targeting different organs and how tea prevents or inhibits most of the cancer. Also went into detail about several cases of mice and rats being injected with black tea after being afflicted with lung cancer from a tobacco carcinogen.
States that green tea and black tea may have different preventative properties because in the case of colon cancer in rats, green tea proved to be more effective. Shows that results can be ambiguous since not enough studies are done in certain cases.
Effects of tea consumption on human cancers
Cited several studies done by different areas which show a correlation between the amount of tea consumed and the effect on a certain type of cancer. However, results are not conclusive since only associations and correlations are observed.
Pretty much the results from Asians who drink primarily green tea are more positive than the infrequent results from Europeans who mostly drink black tea. This could be due to a variety of factors including the fact that green tea has a higher concentration of catechins or due to the genetic and geographical differences between the two areas of the people studied.
Stated that compared with the stronger results obtained from studies with animals, the effect of tea as a cancer preventative in humans are not as clear-cut or precise or conclusive which may be due to a variety of factors including the lifestyles of different people or the smaller quantity of tea drank by humans as compared to animals.
Absorptions and distribution of tea polyphenols
Different compounds have different effects when being injected intravenously versus intragastrically, noted by the differences in Beta elimination half-lives in the plasma.
A pattern of increasing and decreasing concentrations of the compounds in various organs of the rats are observed after oral consumption.
Blood and saliva levels in humans
Studies using human volunteers involving ingestion of a certain amount of compounds found in tea and measuring the plasma concentrations, half-life retention and concentrations in various tissues after certain time periods indicate that the amount of catechins found in heavy drinkers may be comparable on the same scale as the mice used for testing.
Studies using six human volunteers showed that slowly drinking tea is the most effective way of having the greatest amount of catechins delivered to the esophagus since certain compounds are converted to another form only in the oral cavity.
Studies with cell lines
Various cell lines are found to be inhibited at different rates by different polyphenols but the level of inhibition in cell lines are a few magnitudes smaller than would be found in the human plasma.
Possible mechanisms for the inhibition of cell growth by tea polyphenols may involve apoptosis or the disruption of the cell cycle or inhibition of the signal transduction pathway.
Possible active components and their bioavailability
EGCG and EGC are considered as the possible active components of tea extracts because cancer inhibitory activities were demonstrated and they are also the most bioavailable components.
Four different catechins played a role in the inhibitory activity of different cancer cell lines with EGCG as the most active.
Theaflavins and other components also contribute to the inhibition of cancer growth lines but none has been as extensively studied as the EGCG.
Possible mechanisms for the inhibitory actions of tea on tumorigenesis
Not a lot of studies were done but of those that were, many feel that it is more important to take into account the activities of low tissue concentration rather than higher levels.
Mechanisms may involve the antioxidative properties of tea polyphenols or their prooxidant activity since many factors causing cancer are related to O2 species and prooxidant polyphenols may induce apoptosis in cells. There have not been a lot of studies done that involve other mechanisms that relate to the immune system or carcinogens.
Another possible mechanism which has been demonstrated recently may involve the interruption of signal transduction pathways relating to growth.
I’m contemplating doing my final paper on some aspect of cancer research, either current treatments of adult acute myeloid leukemia or something more specific such as the cancer preventative actions of tea extracts.
The article I’m summarizing is called Tea and Tea Polyphenols in Cancer Prevention
Tea and tea polyphenols in cancer prevention
Yang, Chung S;Chung, Jee Y;Guang-yu;Yang;Chhabra, Saranjit K;Mao-Jung, Lee
The Journal of Nutrition; Feb 2000; 130, 2S; ProQuest
pg. S472
This is the link to the pdf http://search.proquest.com.ezproxy2.library.drexel.edu/docview/197454913/fulltextPDF?accountid=10559
Introduction
Tea constituents and their biochemical properties
Inhibition of carcinogenesis by tea in animal models
Effects of tea consumption on human cancers
Absorptions and distribution of tea polyphenols
Blood and saliva levels in humans
Studies with cell lines
Possible active components and their bioavailability
Possible mechanisms for the inhibitory actions of tea on tumorigenesis